Breast cancer is expected to cause 39,510 deaths of American women in 2012 and 450,000 deaths globally. Once breast cancer has spread, it is essentially incurable. A critical barrier to treating advanced breast cancer is the lack of cancer-specific drugs that are effective in a large percentage of cancer patients and have low toxicity. Sixone Solutions, LLC proposes to evaluate the feasibility of a novel approach to developing widely effective, low toxicity breast cancer drugs. Previous work established that a transcriptional complex, consisting of proteins Eya and Six1, plays a significant role in causing cells to become cancerous and spread. These proteins are important in early embryo development and are essentially absent in normal adult cells. However, in certain cancers, including breast cancer, they reemerge. Many breast cancers have been shown to have high levels of these proteins. Genetic manipulation to reduce Eya and Six1 levels causes cultured cancer cells to act more like normal cells and significantly inhibit tumor growth and spread in mouse models. The Phase I project is designed to determine if the same effect can be achieved pharmacologically. The Eya protein has phosphatase activity that is essential to the cancer-causing potential of the Eya/Six1 complex. The active site of this phosphatase is different from most other cellular phosphatases, which offers a unique target. Our affiliated university investigators have identified a class of novel small molecules that inhibit the Eya phosphatase but not other cellular phosphatases. The proposed Phase I project will determine if these compounds can block the proliferation, survival, and metastatic activities of Eya/Six1. Cell culture assays will assess the impact of the compounds on non-cancerous mammary epithelial cell lines and mammary carcinoma cells with medium to high levels of Eya and Six1. In vivo assays will assess metastasis and chemosensitization in mice injected with breast cancer cells and treated with compound. If the Phase I project is successful, it will establish the feasibility f developing drugs to treat breast cancer, and possibly other cancers, through a new approach. Because the target proteins are overexpressed in a large percentage of breast cancers and because they are absent or minimally expressed in normal tissues, this approach could be broadly effective in a large number of breast cancer patients and have low toxicity, addressing the current needs in treating advanced breast cancer. In addition, small molecule inhibitors should be less expensive to manufacture that the current antibody-based breast cancer therapeutic.